Field of the Invention
This invention relates to a hydrostatic drive system with a hydrostatic pump which is driven by a drive motor and is connected in a closed circuit with a hydrostatic motor. The hydrostatic motor is in a drive connection with a consumer. The closed circuit is formed by a first hydraulic connection and a second hydraulic connection. A pressure accumulator device can be connected with the two hydraulic connections for the storage of energy and the discharge of energy.
Description of Related Art
Hydrostatic drive systems in a closed circuit are used for the drive of a consumer in vehicles such as motor vehicles or public transit vehicles, e.g., buses, preferably for urban mass transit, and for mobile self-propelled machines, in particular industrial trucks, agricultural machines, forestry machines and construction machines, such as, for example, excavators, wheel and telescoping loaders, tractors, combine harvesters, forage harvesters, sugar beet and potato harvesters.
With a pressure accumulator device (for the storage of energy and the discharge of energy) that can be connected with both hydraulic connections of the closed circuit, a hybrid drive concept and, thus, a hybrid function can be realized in a hydrostatic drive system with a closed circuit. The consumer can be driven in a drive phase with the energy in the pressure accumulator device during a discharge operation of the pressure accumulator device. If the pressure accumulator device is operated in a charging operation during a braking or deceleration phase of the consumer and is charged with hydraulic fluid, energy can be recovered during the braking or deceleration of the consumer.
In a hydrostatic drive system in a closed circuit, it should be ensured that during the charging operation of the pressure accumulator device, during which a determined amount of hydraulic fluid is removed from the pressure accumulator device out of the high-pressure-side hydraulic connection of the closed circuit, the corresponding quantity of hydraulic fluid is made up at the low-pressure-side hydraulic connection of the closed circuit. Correspondingly, during discharge operation of the pressure accumulator device, during which a determined quantity of hydraulic fluid is fed from the pressure accumulator device to the high-pressure-side hydraulic connection of the closed circuit, it should be ensured that the corresponding quantity of hydraulic fluid is diverted from the low-pressure-side hydraulic connection of the closed circuit.
To make possible this quantity and volumetric balancing at the low-pressure-side hydraulic connection of the closed circuit during the extraction or the addition of a quantity of hydraulic fluid at the high-pressure-side hydraulic connection by the pressure accumulator device, it is known that the pressure accumulator device can be formed by a high pressure accumulator and a separate low pressure accumulator. DE 10 2007 012 121 A1 describes a generic hydrostatic drive system with a pressure accumulator device that has a high pressure accumulator and a separate low pressure accumulator that compensates for the hydraulic fluid volumetric flow of the high pressure accumulator, which is extracted or added at the high-pressure-side hydraulic connection of the closed circuit, on the low-pressure-side hydraulic connection.
In DE 10 2007 012 121 A1, the high pressure accumulator of the pressure accumulator device can be connected with the respective high-pressure-side hydraulic connection of the closed circuit. Correspondingly, the separate low pressure accumulator of the pressure accumulator device can be connected with the respective low-pressure-side hydraulic connection of the closed circuit. A pressure accumulator device of this type with two separate pressure accumulators is complex and expensive to build and takes up a great deal of space, as a result of which the hybrid function of the pressure accumulator device entails a high level of expense and effort for the construction and operation of the system.
Therefore, it is an object of this invention to provide a hydrostatic drive system in which the hybrid function of the pressure accumulator device has a simple, compact, and economical construction.